Any quality UPS with more than a few hundred VA of backup power should be able to handle the transient voltage sags being discussed by the original poster. I'd stick with APC, personally. You can pick up a 1500VA unit for under $200 if you shop around. I was using a APC Matrix 5Kva unit for my theater system in my old house. That way, my components never saw anything but a clean 120v sine wave. Due to older home/wiring, the voltage was otherwise all over the place whenever the AC would come on, the fridge compressor cycled on, microwave turned on, hair dryer, etc.

Best,